Everything you need to know about autoflowers: a grow guide

Growing autoflowers: an autoflowering grow guide


I think this section is the do or die between having a great auto crop or a disaster. Autoflowers have such a short vegetative growth period and the final plant is rarely very big. Get it wrong and you’ll end up with a lollipop stick of bud. That’s why I think that whilst autos fulfill a gap in the outdoor growers repertoire (after all its damnably difficult to control the light/dark cycle of the sun), if you can its best to start them off indoors under lights. You just maximize the level of control that way. Before you start growing autoflowers, please read our piece on how to grow autoflowers 


“Once you pop ’em you can’t stop ’em”

Effectively this means that whilst the answer is “yes”, the autos have a genetically limited life: from the moment the cannabis seed germinates it will progress through its short vegetative stage and speed onto flowering. As the “mother” plant won’t be big enough to take a clone until she is around 5 weeks old, once you have added a week whilst the clone roots, the clone thinks of itself as 6 weeks old and upward vegetative growth will have finished. Despite being tiny, the cutting will finish flowering at the same time as the mother more or less – here’s one I tried for a laugh:

The problem is, there is NO WAY to extend autoflower growth by keeping it in veg stage. Any clone taken from an auto flower will be the same age as its mother – but without the growth.


Start off with a little veg feed at around week 2 and slowly increase the amount of feed as the plant develops up to (depending on the auto) around week 6 or even 7. Wait to switch to flower food until after the cannabis plant has noticeably stopped its upward growth, even though she may have been flowering for a week or so beforehand.


You can grow autos on 24/0 but I think its good to let them have a little rest time and electric consumption is also a issue. I grow mine for the first two weeks under a 120 watt draw Fero LED for the first couple of weeks and I tend to keep that on for 21/3 with the LED grow light around 70 -80 cm away from the seedlings. When then they are potted on to the 13 cm sexing pots and put under my larger LEDs I then change the lighting schedule to 18/6 where it will remain until I crop. 

Many people choose to grow autoflowers with CFLs. There’s no reason why you should use CFL over HPS or LED, but autoflowers appeal to CFL growers. You can read our full guide to growing autos using CFLs here.

Pruning? Can you prune autos?

Yes you can but pruning cannabis autos needs to be done in the very early stages as it holds the plant back in that critical time. I’ve experimented over several crops with this and my advice would be that you are better off not pruning autoflowering marijuana as in most cases the plant will end up giving less weight. That said, you can break the apical dominance and encourage vigorous side branching by “knuckling” if you are using a longer term variety such as the “Cream Caramel” (yes Sweet Seeds, I know you say this is an 8-weeker, but every one I’ve grown has gone to 12 weeks plus).


Lets assume your environmentals are all good, with light at around 400watts a m2, temps at around 23ºc, humidity 55% for flowering and you are replenishing your air every couple of minutes whilst maintaining a good nutrient regime and getting plenty of O2 to the roots etc etc (who ever said growing great smoke was easy?)

The simple answer is : it depends on how long the plants are going to take. The 9 week varieties such as MI5 (Shortstuff) average around 40g a plant (dried weight) under my fero led lights at 10 per m2; an 11 weeker autoflower such as DInafem’s XXL range yields an average of 100g dry weight, and the longer super varieties such as Chase (15 weeks) 150g -500g a plant outdoors.

High yielding autoflower strains take longer from seed to harvest than fast autos. You’re trading off a quick succession of crops with amount per plant. Generally speaking though, the very fast strains yield so little as to be hardly worth planting more than 1 or 2 to tide you over while you wait for your main harvest.

Growing autos outdoors >>

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